The present invention relates to an end seal for an ink chamber of a printing machine, and more particularly, to an end seal having a longer operating life for use with a flexographic printing machine.
Conventionally, in printing machines, such as flexographic printing machines, an ink transfer or anilox roll transfers ink to an adjacent plate roll for printing. Ink is supplied to the anilox roll from an ink chamber defined by a chamber housing which partially surrounds the anilox roll. Specifically, ink is supplied through an ink supply tube and then through an ink supply line in the chamber housing, into the ink chamber. In like manner, ink is removed from the ink chamber through an ink return line in the chamber housing and then through an ink return tube.
In order to prevent the escape of ink from the chamber, while ensuring that the ink enters the cells in the anilox roll and has a predetermined volume on the anilox roll, doctor and sealing blades are provided at the entry and exit positions of the anilox roll relative to the ink chamber. The blades are fixed to the chamber housing so that the blades overhang the chamber housing and contact the anilox roll.
With this arrangement, the outer surface of the anilox roll passes through the ink chamber and picks up ink for printing. The ink is metered by means of the doctor blade held to the outlet end of the chamber housing, and sealed with a sealing blade held to the inlet end, with the free ends of the blades being in contact with the outer surface of the anilox roll.
A seal is provided at each end of the blade, that is, at each end of an anilox roll for sealing the ends thereof. Examples of such arrangements are shown in U.S. Pat. Nos. 7,597,761; 6,739,248; 6,672,207; and 5,150,651; and U.S. Patent Publication No. 2004/0261640, the entire disclosures of which are incorporated herein by reference.
Each seal is formed by a compressible body. Since the seals provided at each end of the anilox roll function to seal the ends of the ink chamber, each seal must lie against the peripheral surface of the rotating anilox roller. As a result, each seal is therefore exposed to mechanical stresses as well as wear. Further, during the printing operation, the blades, which press against the anilox roll, also wear. The geometry of the sealing function between the anilox roll, the two blades and the end seal changes.
Conventionally, each end of a blade sits upon a flat supporting area of the respective seal. As a result, there is not much flexibility at the opposite ends of the blades where they are held by the chamber seals. Because there is more force by the seals on each blade, that is, at the ends of the blades where they are held, the ends of the blades are less capable of flexing or bending at these points. As a result, there is uneven wear on the ends of the blades adjacent the seals, which tends to cause more wear and more leakage of ink at the ends of the anilox roll. Further, ink tends to ride under the blade, that is, between the blade and the flat supporting area of the seal, causing the blade to lift up away from the seal, thereby resulting in still more leakage. Thus, the place where the seal, anilox roll and blades join, is particularly susceptible to leakage.